Petrels are smaller cousins of the albatrosses. Found throughout the world’s oceans from tropical to polar latitudes, they nest on remote islands naturally free of mammalian predators. The largest populations are found in the Southern Ocean where they play important roles in marine and terrestrial island ecosystems. Petrels consume prey volumes equivalent to commercial fisheries, helping to regulate marine food webs, and they transfer the nutrients from their prey to islands. Deposited in guano, these nutrients leach into soils and coastal waters where they fuel productivity.
Almost half of the world’s 124 petrel species are threatened with extinction, predominantly owing to the impacts of invasive predators intentionally or accidentally introduced to islands by humans. On Macquarie Island this caused the local extinction of several petrel species in the 19th and early 20th centuries. Of 14 species known or thought likely to have bred on Macquarie at one time, by the 1970s just three species were found to remain on the main island, albeit experiencing declines, while a further three species were recorded from offshore rock stacks. Listed as threatened species under state or federal legislation as a result, pest management began, resulting in the staged eradications of introduced predators. Wekas, a ground-bird from New Zealand originally introduced as food for people but which devastated populations of smaller petrels by eating eggs and chicks, were eradicated in 1988, cats by 2001, and rabbits, rats and mice in 2011-2014.
As defence mechanisms against other birds like skuas which naturally predate petrels, they nest in under-ground burrows to which they only return at night. These burrows are scattered across challenging terrain, often concealed beneath dense vegetation, all of which makes them very difficult to survey.